Jehu killed the evil king of Judah, Amaziah.  His mother, Athaliah, a daughter of Ahab, proceeded to murder the rest of the royal family, although Jehu disposed of 42 of them in Israel at the well of Beth-Eked.  Her intent was probably to destroy all the lineage of David, thus making void God's promise of a lasting kingship for the house of David.  One baby, Joash, survived because his aunt hid him in the Temple.  Her husband was Jehoida the high priest (2 Chron 22:11).  Joash stayed hidden for 6 years, while Athaliah ruled Judah.  She was a usurper, and the only female ruler of either of the two kingdoms.  Other than murdering all her own grandchildren, nothing else of her reign is recorded in Scripture.  It is implied, however, that she supported the worship of Baal (2 Kings 11:18).  
       
The high priest orchestrated a palace coup.  In this, he utilized foreign mercenary troops, the "Carites."  Compare Kerethites (2 Sam 20:23).  Jehoida showed the boy king to the temple guards, then crowned him, and anointed  him.  When Athaliah came to see what the fuss was about, she was slain with the sword.  But Jehoida carried on with a fullscale revolution.  He made a covenant between God, the king and the people that they would once again be the Lord's people.  The people then rushed upon the temple of Baal, destroyed it and killed its priest.

       

The long rule of Joash represented a partial restoration of the true faith of Israel -- at least so long as Jehoida lived.  And he lived a long time -- 130 years! (2 Chron 24:15).  To Jehoida, rather than Joash, belongs the credit for the renewal of the covenant, indeed for the resurgence of the very idea of a covenant people.  The Bible speaks at length about the rebuilding of Solomon's Temple, however, there must also have been a corresponding emphasis on worship according to the Law.  Guilt offerings are mentioned in 2 Kings 12:16.

       

Yet Judah was weakened, it could not stand against external enemies.  Like Israel,  it was the ready prey of Aram to the north.  Hazael reached south as far as the Philistines, and also threatened Jerusalem.  Joash lacked the strength to fight him, so took all the valuables that he could find in the Temple, and bribed Hazael to leave him alone.  

       

Like Solomon, Joash turned away from God towards the end of his reign.  Jehoida's son, Zechariah, prophesied against the disobedience of the leaders of Judah.  Joash ordered him stoned to death (2 Chron 24:20-22).  God's retribution did not delay.  An army from Aram invaded Judah, killed the leaders of Judah, and wounded Joash (2 Chron 24:23-25).  2 Kings says that his officials assassinated him while he was out of town (2 Kings 12:20).  2 Chronicles says they murdered him in his bed (2 Chron 24:25).  A sad end to a reign that began with a renewal of righteousness.